(1) Field of the Invention
This invention relates to photoinhibitors and their use in photopolymerizable compositions, and to methods of producing positive and negative polymeric images from these compositions.
(2) Description of the Prior Art
Recently polymeric imaging systems which provide a positive polymeric image have been developed. One such system is described by Pazos in U.S. Pat. No. 4,198,242. In this system
(a) a substrate is coated with a photopolymerizable composition containing PA1 (b) the photopolymerizable coating is exposed through a process transparency to radiation, at least some of which has a wavelength less than 380 nm whereby the nitroaromatic compound is dissociated to a polymerization-inhibiting nitroso monomer in the radiation-struck areas, and PA1 (c) a greater portion of the photopolymerizable coating is exposed to radiation substantially limited to wavelengths greater than 380 nm whereby a positive polymeric image is formed in the areas struck by the second radiation but not struck by the first imagewise radiation. PA1 (a) a normally nongaseous, ethylenically unsaturated compound capable of addition polymerization by free-radical initiated chain propagation, PA1 (b) about 0.004 to about 0.7 part by weight, per part of component (a), of an acidic o-nitroaromatic compound of the formula ##STR1## wherein R.sup.1 .dbd.R.sup.4 .dbd.H or the residue of a second benzene ring as defined below; and at least one of R.sub.2, R.sub.3, R.sub.5 or R.sub.6 must have a carboxylic acid functionality as indicated below; PA1 (c) about 0.001 to about 10 parts by weight, per part of component (a), of an organic, radiation-sensitive, free-radical generating system which is activatable by actinic radiation that does not significantly rearrange the acidic o-nitroaromatic compound to an inhibitor of free-radical polymerization. PA1 (a) Coating from water (dilute ammonium hydroxide) is possible, and PA1 (b) better latent image stability is obtained than with the currently used photoinhibitor. PA1 (1) coating the substrate with the above photopolymerizable composition, PA1 (2) imagewise exposing a portion of the photopolymerizable coating through an image-bearing transparency to radiation, at least about 20% of which has a wavelength of about 200 to about 380 nm, thereby rearranging at least some of the acidic o-nitroaromatic compound to polymerization-inhibiting nitroaoaromatic compound, and PA1 (3) subjecting the coating to a second exposure, whereby a greater portion of the coating, including the portion exposed during the imagewise exposure, is exposed to radiation substantially limited to wavelengths greater than about 380 nm, whereby a positive polymeric image is formed in the areas exposed during the second exposure, but not exposed during the imagewise exposure. The image formed in step (3) is developed by removing the unpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation, or by differential adhesion of a pigment toner to the saie unpolymerized portion of the coating. PA1 (1) coating the substrate with the above photopolymerizable composition, and PA1 (2) imagewise exposing a portion of the photopolymerizable coating through an image-bearing transparency to radiation substantially limited to wavelengths greater than about 380 nm, whereby a negative polymeric image is formed in the areas exposed to the radiation. PA1 R.sub.1 and R.sub.2, taken together, are --OCH.sub.2 O--; PA1 R.sub.4 is aryloxy of 6 carbons substituted with carboxyl, or (CH.sub.2).sub.x CO.sub.2 H where x=2-12, and x.noteq.2 or 3 when R.sub.3 is OH.
(1) a nongaseous, ethylenically unsaturated, polymerizable compound, PA2 (2) 0.001 to 10 parts by weight per part of polymerizable compound of an organic, radiation-sensitive, free radical generating system, and PA2 (3) 0.004 to 0.7 parts by weight per part of polymerizable compound of a nitroaromatic compound, and PA2 R.sup.2, R.sup.3, alike or different, are H, OH, halogen, NO.sub.2, alkyl of 1 to 18 carbons, alkoxy in which the alkyl is of 1 to 18 carbons, acyloxy of 2 to 7 carbons, aryl of 6 to 18 carbons, benzyl, halogen-substituted phenyl, polyether of 2 to 18 carbons and 2 to 10 oxygens, dialkylamino in which each alkyl is of 1 to 18 carbons, thioalkyl in which the alkyl is of 1-18 carbons, thioaryl in which the aryl os of 6 to 18 carbons, or --O(CH.sub.2).sub.x CO.sub.2 H or (CH.sub.2).sub.x CO.sub.2 H where x=1 to 12; PA2 R.sup.2 and R.sup.3, taken together, are --OCH.sub.2 O-- or --O--(--CH.sub.2 CH.sub.2 O)--.sub.q in which q is an integer from 1 to 5; PA2 or any two of R.sup.1, R.sup.2, R.sup.3 and R.sup.4, taken together, are the residue of a second benzene ring fused into the benzene nucleus, with the proviso that not more than one of R.sup.2, R.sup.3 is OH or NO.sub.2 ; PA2 R.sup.5 is H, a C.sub.1 -C.sub.18 alkyl, OH, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons, PA2 R.sup.6 is H; alkyl; phenyl; alkoxy in which the alkyl is of 1 to 18 carbons; aryloxy of 6 to 18 carbons, either unsubstituted or substituted with halogen, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, or --COOH; (CH.sub.2).sub.x CO.sub.2 H where x=1-12 and x.noteq.2 or 3 when R.sub.5 is OH, with the proviso that only one of R.sup.5 and R.sup.6 is H; or PA2 R.sup.5 and R.sup.6 together are .dbd.O or --O--C.sub.2 H.sub.4 --O--; with the proviso that carboxyl is excluded on the ring containing the nitro group and neither R.sub.5 or R.sub.6 is carboxyl.
Although this system can produce excellent positive polymeric images, the photoinhibitor generally is not soluble in aqueous coating solutions and there is room for improvement in the stability of the latent image during hold times between the untraviolet and visible exposures.